Femtosecond Ligand/Core Dynamics of Microwave-Assisted Synthesized Silicon Quantum Dots in Aqueous Solution

Abstract

A microwave-assisted reaction has been developed to produce hydrogen-terminated silicon (Si) quantum dots (QDs). The Si QDs were passivated for water solubility via two different methods: hydrosilylation produced 3-aminopropenyl-terminated and a modified Stöber process produced silica-encapsulated Si QDs. Each method produces water soluble QDs with maximum emission at 414 nm and after purification exhibit intrinsic fluorescence quantum yield efficiencies of 15 % and 23 %, respectively. Even though the QDs have different surfaces, they exhibit near identical absorption and fluorescent spectra. Femtosecond transient absorption spectroscopy was used to temporally resolve the photoexcited carrier dynamics between the QDs and ligand. The transient dynamics of the 3-aminopropenyl-terminated Si QDs is interpreted as a formation and decay of an excited-state charge transfer (CT) state between the delocalized π electrons of the carbon linker with the Si core excitons. This CT state is stable for ~4 ns before reverting back to a more stable long-living species. The silica-encapsulated Si QDs show a simpler spectrum without CT dynamics.

Chemical Insight into the Origin of Red and Blue Photoluminescence Arising from Freestanding Silicon Nanocrystals

“…, τ < 10 ns) inconsistent with a band gap transition have been reported for these Si NCs. 42,43 XPS analysis of Si NC-B shows expected Si, O and C elemental signatures as well as a low intensity emission in the N 1s spectral region (Fig. 2D–E).…”

NaRb7(Si4–xGex)2 – Soluble Zintl Phases Containing Heteroatomic Tetrahedral ­[Si4–xGex]4– Clusters

“…[29] Furthermore, the Na 4 Si 4 phase has been used for the synthesis of Si nanoparticles. [30,31] The access of mixed Si/Ge phases NaRb 7 (Si 4-x Ge x ) 2 in combination with their solubility offers interesting ways and synthetic alternatives for the formation of mixed Si/Ge nanoparticles. As a new type of soluble Zintl phase that solely contains tetrahedral group 14 clusters is identified, the large variety of reactions already known from nine-atomic Zintl clusters can now be extended to the tetrahedral analogues.…”

Colloidal silicon quantum dots: synthesis and luminescence tuning from the near-UV to the near-IR range

“…3-Aminopropenyl terminated silicon QDs were produced by a simple microwave-assisted reaction. They had a crystalline structure and an average diameter of 3.4 ± 0.7 nm covering the emission in the NUV–blue range [70, 71]. …”